1. Field of the Invention
The present invention relates to a surface mounting discharge tube to be directly soldered on a printed circuit board.
2. Description of the Related Art
In general, a discharge tube is comprised of a cylindrical ceramic envelope sealed at its two ends by side surfaces of electrodes. It has been mounted on a printed circuit board in the past through lead wires provided at the end faces of the electrodes.
Mounting through lead wires means mounting the discharge tubes one at a time. There are however increasing demands for mounting a large number of discharge tubes all at once. Therefore, surface mounting directly on the printed circuit board without using lead wires has become necessary.
At that time, if just placing a cylindrical discharge tube as it is on a printed circuit board, it will roll around making positioning difficult. Therefore, the practice has been to provide flat parts at parts of the electrodes. See Japanese Unexamined Utility Model Publication (Kokai) No. 59-33690 (claims and FIGS. 2 to 5) and Japanese Unexamined Patent Publication (Kokai) No. 2003-151716 (claims and FIGS. 1 and 3). Further, surge absorbers, which have the same basic structure as discharge tubes, have been provided with electrodes of polygonal shapes for the same purpose. See Japanese Unexamined Patent Publication (Kokai) No. 2001-135453 (claims and FIG. 3).
Surface mounting means to place solder pallets at mounting positions on the printed circuit board, place the discharge tubes so that the soldering use flat parts at the peripheral edges of the electrodes are positioned there, insert the assembly into a heating furnace to melt the pallets, then remove the assembly and allow the solder to solidify for completing the bonding process.
However, such surface mounted discharge tubes suffer from the problem of positional deviation from the predetermined mounting positions at the time of soldering and therefore insufficient reliability in terms of pressure cooker test (PCT) properties etc.